Drop-forged rotor



May 23, 1939. c. F. REIS DROP-FORGED ROTOR Filed Jan. 10, 1938 FIG. 1.

INVENTOR CURT F. REIS BY [60M ATTORNEY Patented May 23, 1939 UNITED STATES PATENT OFFICE 2 Claims.

This invention relates to improvements in magneto rotor construction, and more particularly to an improved low cost construction of rotor for magneto-electric machines of so-called rotating field type.

The present invention has as its primary objective, the production of a more rugged, dependable, low-cost rotor for magnetos of the type referred to, characterized by a drop-forged rotor frame construction, and an assembly not necessarily involving the use of casting operations of any kind, with the possible exception that the permanent magnets, pole pieces or magnet bars may be initially formed by casting prior to assembly of the elements of the rotor.

Yet another object of the invention is attained in the production of a rotor for magnetos of rotating field type, which may be formed to include a frame structure of drop-forged metal, and which is characterized by a minimization of length or axial dimension, and serves to dispense with magnetic bridging plates, end plates, or comparable elements often heretofore employed in rotors for rotating-field type magnetos.

Yet another object of the invention is attained in an improved method of forming certain of the parts of a rotor for a machine of the type referred to, and which effects certain assembly economies and improves the integration of the structure, by drop-forging a complete shaft element together with end plates formed integrally therewith in a single forging operation, and optionally as a part of the unitary forged structure, an intermediate structural support or bridge for the pole-shoe members.'

The foregoing and numerous other objects will appear as the description proceeds, when considered in connection with the accompanying drawing of a presently preferred structural embodiment of the invention. In the drawing:

Fig. 1 is a side elevation of a complete rotor formed in accordance with the method to be described, and embodying a structure resulting from the invention; Fig. 2 is a sectional elevation of the device as it would appear when viewed along line 2-2 of Fig. 1; Fig. 3 is an axial section of the rotor of Fig. 1, as would appear when viewed along line 3-4 of Fig. 2; Fig. 4 is a transverse sectional elevation taken along line 4-4 of 0 Fig. 1, and Fig. 5 is a section of the device as ent example may be said to embody all of the elements of the completed rotor but for the pole pieces or magnets together with pole shoes and assembly elements such as rivets, includes as an integral drop-forged structure a shaft portion 5 including a drive end l0 provided with a reduced threaded extremity H for the reception of a gearor coupling-holding nut or the like (not shown) the shaft portion [0 is tapered between the part l2 of normal diameter and the threaded end ll, so as to form a tapered fit for the reception of the coupling member in case an impulse coupling is utilized. Intermediate shaft portions l3, also parts of the integrally formed drop forged structure, lie at opposite sides of a central spacer l5, this element serving as a structural bridge between the pole shoes, as will hereinafter appear. The metal of the forging is diametrically extended to form a pair of end plate members, one thereof appearing at I6, near the driving end, and the other plate portion H being located near the opposite end of the rotor. Just beyond the plate I! is a relatively enlarged shaft portion l8. Either the portion l8 or a free end l9 therebeyond, may be used, according to frame design of the machine, as a journalled portion for this end of the shaft. The portion i9 may also at the time of or after drop-forging the frame, be formed or shaped to constitute a breaker cam, if so desired.

In the assembly presently described by way of illustration, the pole pieces, being of bar form and preferably circular in section, are four in number, and are arranged transversely of the axis of the rotor, being arranged in pairs at opposite sides of the axis. The magnet bars are indicated at 20, being suitably arranged with respect to their polarity, as well understood. It is my great preference to employ for the magnet bars, an alloy characterized by high coercive force and retentivity, among the materials particularly suitable for the purpose being certain of the alloys known as Alnico steel.

Proceeding now to a, description of the pole shoes, in the present example two thereof are utilized, and are diametrically and peripherally disposed in assembly, being indicated at 22 and 23. Each pole shoe is provided with a number of recesses or sockets 25 corresponding to the number of magnet bars or pole pieces employed. Each of the pole shoes is further of laminated construction as will appear, the laminations being compressed prior to assembly of the shoes into the rotor, and the assembly constituting each shoe, drilled say in a multiple drill, to provide the requisite number of sockets or recesses, each conforming in its internaldiameter fairly closely to the external diameter of the end of the associated bar magnet, whereby there results a close or press fit between the shoes and the ends of he magnets so as to insure a uniformly good flux path between these elements.

Suitable temporary holding means (not shown) being provided for retaining the shoes in assembly over the ends of the pole pieces, this sub-assembly is then definitely positioned within the dropforged frame as described. Permanent assembly is effected, preferably by drilling through the shoes and the end plate portions I6 and I! to provide passages or bores for assembly rivets 30. With the parts thus far referred to suitably held in a jig or the like, the rivets 30 are inserted and their opposite ends upset or headed into countersunk recesses 3| in the end portions I6 and I1 respectively.

In the form of rotor shown and embodying cylindrical magnet bars or pole pieces 20 of substantialsize, it has been found desirable to pro vide the spacer I5 as a structural bridge for the intermediate portions of the shoe assemblies 23. However, in a rotor for a smaller machine or one requiring only magnet bars of smaller size, it is entirely feasible to construct the rotor frame by drop-forging, and to omit the intermediate spacer element I5. In the example illustrated utilizing the element I5, the pole shoes are each desirably provided with a rectangular or other suitable form of recesses 35 which provides for a rigid interfitting engagement between the shoes and the center support. This recess may be provided by utilizing the requisite number of laminations or punchings in the central portion of each of the shoes, of a suitably reduced width, or so notched as to accommodate the ends of the center support I5. This provides a definite saddled relation between the shoes and their support, and besides making for structural rigidity of the rotor assembly, the support I5 is so selected as to length or dimension transversely of the rotor axis, that it receives and takes any compression stresses during and after assembly and thus relieves the magnet bars of any strains resulting from endwise compression thereof. This is highly desirable in the case of pole pieces formed of certain alloys characterized by a relatively course crystalline structure, wherein for both structural and magnetic reasons it is desirable to obviate any substantial compression stresses.

In case the rotor is formed according to a design in which the center element I5 is omitted, it is a preference so to regulate the length of the bars with respect to the distance between the bottoms of opposed bar sockets, that the end plates, such as I6 and I1, receive any compression stresses incident to the assembly.

By way of reviewing the major steps involved in the construction of the rotor or rotors herein described, it may be noted that the rotor frame, including as an integral structure, the portions I2, I3, I5, I6, II, I8 and I9, is or may be formed, preferably of a relatively non-magnetic metal, such as a brass or other suitable non-magnetic alloys susceptible of formation by drop-forging, the elements noted being formed up by further preference, in a single drop-forging operation, the stock from which the forging is formed being heated to the extent, according to the alloy utilized, necessary to enable it to be drop-forged. The forging impact is preferably in a direction normal to the axis of the finished rotor. Following formation and any necessary machining, for example, cutting the threads on the shaft end II, or any machining desired for shaping a breaker cam on the opposite end of the shaft, the pole shoes 22 and 23 are drilled or otherwise recessed to receive the ends of the magnet bars, and are then assembled to the bars and held in a suitable jig prior to and during assembly into the dropforged rotor frame. Final assembly is completed, as heretofore briefly mentioned, by secure attachment through the use of rivets III or an equivalent thereof. Either before assembly of the shoes and bars to the frame, or thereafter, any external machine operations may be effected on the exposed portions of the rotor.

As will appear from the drawing, it is my preference to extend at least one, say the central rivet 30 of each group, through the bridge or spacer element I5. This may be done either by providing recesses or openings, shown at 34, in the end portions of the spacer element. This arrangement offers a distinct structural advantage in an increased torsional rigidity of the cage or frame, and hence of the rotor itself, the arrangement being particularly desirable in the event an impulse coupling is utilized for connecting the magneto to the associated engine.

The present disclosure has included no detailed or specific description of the remaining parts of the magneto, as they are or may be of any of a number of suitable types and arrangement. As an example of a magneto frame, winding, distributor, breaker assembly, etc., with which a rotor of the present type is adapted for use, attention is directed to my copending application Serial No. 184.207, filed January 10, 1938. The magnetic and electrical circuits of the completed machine embodying the rotor of the present invention may, however, be conventional, and will readily be understood by those skilled in the art.

The production of a rotor cage or frame by drop-forging has, of itself, been known and utilized heretofore, having been disclosed and made the subject of claims in U. S. Letters Patent No. 2,059,745, issued to'this' applicant November 3, 1936. However, in the earlier design, the magnet bars were positioned in their final relation and while so positioned, the body of holding metal constituting the cage or frame. was dropforged about the magnets. However, with the advent of magnetic alloys characterized by improved magnetic properties, but which are, by reason of internal metallic structure, sensitive to compressive stresses, there has arisen a need for a drop-forged rotor construction in which the frame, although forged, is initially formed, and the magnet bars assembled into the frame after forging. The method and structure thus outlined by the present disclosure is accordingly the reverse of, and hence fully distinguishable from the method or process described and claimed in Patent 2,059,745.

It will have appeared from the foregoing description and the accompanying drawing, that magneto rotors formed in accordance with the present principles, fully attain each of the several objects hereinabove mentioned, as well as in many others, and that the invention has resulted in a magneto rotor for machines of rotating field type, constituting a distinct advance in the art.

Although the invention has been described by making detailed reference to a specific embodiment of the invention selected for purposes of patent disclosure, this description is to be understood entirely in a descriptive sense, and not with any limitations in meaning, except such as may be imposed by the claims hereunto appended.

I claim as my invention:

1. In a. rotor structure for magnetos of rotating field type, an assembly of permanent magnets of bar form disposed parallel to each other, and substantially transversely of the rotor axis, a pole shoe overlying each end of the magnet assembly, a drop-forged cage or frame for the rotor, formed of a non-magnetic metal and including a stub shaft portion for each end of the rotor, an intermediate shaft portion, a pair of end plates of substantially circular form spaced from each other and located inwardly of the stub shaft portions, a center spacer bar substantially normal to the intermediate shaft portion and between the end plates, the bar magnets and pole shoes being assembled into the cage between the end plates, with the shoes in abutting engagement to the center bar, and elongate holding elements extending through the shoes and end plates and serving to secure the plates and shoes into the cage.

2. In a rotor structure for magnetos of rotating field type, an assembly of permanent magnets of bar form disposed parallel to each other and substantially transversely of the rotor axis, a pole shoe overlying each end of the magnet assembly, a drop forged cage or frame for the rotor, formed of a non-magnetic metal and including a stub shaft portion for each end of the rotor, an intermediate shaft portion, a pair of end plates of substantially circular form spaced from each other and located inwardly of the stub shaft portions, a center spacer bar substantially normal to the intermediate shaft portion and between the end plates, the bar magnets and pole shoes being assembled into the cage between the end plates, with the shoes in engagement with the center bar, elongate holding elements extending through the shoes and end plates whereby to secure the plates and shoes into the cage, the pole shoes being of laminated construction and recessed from their inner faces so as interfittingly to receive the ends of the center spacer bar and the ends of the bar magnets.

CURT F. REES. 

